There has been disclosed a hydrogen engine system mounted in a vehicle, including a plurality of intake pipe sections forming intake passages communicating with a plurality of combustion chambers, an intake pipe collecting section connected with these intake pipe sections to form a collecting space which is a space where these intake passages are collected, a plurality of first injection valves that inject one of hydrogen and oxygen to either the plurality of combustion chambers or the plurality of intake passages, an intake connection passage constituting section having one end connected with the intake pipe collecting section to form one intake connection passage communicating with the collection space, and a second injection valve that injects the other of hydrogen and oxygen to a predetermined region of the intake connection passage (see Patent Literature 1).